1. Field of the Invention
The present invention relates to a bridging circuit for translating between signal formats. More particularly, this invention relates to a bridge for translating between a Universal Serial Bus (USB) signal format and a Peripheral Component Interconnect (PCI) signal format.
2. Description of Related Art
A USB provides a high bandwidth serial bus for connecting numerous peripherals (such as external CD-ROM drives, printers, modems, mice, keyboards, and so forth) to a PC through a single, general-purpose port. The USB format supports hot plugging, automatic device identification, and multiple data streams. There are presently three USB speeds, low speed (1.5 Mbits/sec), full speed (12 Mbits/sec), and high speed (480 Mbits/sec).
A PCI local bus allows PCI-compliant expansion cards to be installed in a computer. The PCI specification allows I/O cards to be automatically identified and configured by the host system without user intervention. The PCI format provides a standard, common bus connection for a plethora of Input/Output (I/O) interface chips.
FIG. 1 is a schematic block diagram of a conventional PCI-based USB host controller 10. Referring to FIG. 1, a conventional PCI-based USB host controller 10 provides USB ports 14 to a host computer through a PCI bus 12. The PCI-based USB host controller 10 may be attached to the PCI bus 12 either through an expansion slot as an I/O card, or permanently attached on the system's main circuit board. In these controllers, the PCI interface 16 is the primary initiator of action in the system, with the USB interface 18 operating as a root hub.